Rotary electromagnetic positioning device



Sept. 23, 1952 H. B. AcKl-:RMAN

ROTARY ELECTROMAGNET'IC PosTIoNING DEVICE Filed Dec. 29, 1949 FIG. 3

ATTORNEYS Patented Sept, 23, 1952 g UNITED STATES PATENT OFFICE HowardB. Ackerman, Rockville Centre, N. Y. Application December 29, 1949,Serial No. 135,647

14 claims. l

My invention relates to improvements in rotary electromagneticpositioning devices for accurately positioning various other devices.

I have conceived of the device under consideration as being useful inconnection with the turning of the tuning dial of an aircraft radio,particularly for tuning-in any desired station instantaneously. It is tobe understood, however, that my improved rotary positioning device maybe used for positioning various devices such as hydraulic valves, steamheat controls for railroad cars, switches and other devices and controlsfor instruments whether located close at hand or at a distance.

The primary object of my invention is to provide a rotaryelectromagnetic positioning device having amagnetic rotor which may beturned to any selected angular position for which the device isconstructed and wherein all the coils of the stator are energizedsimultaneously for each angular position so selected. A further objectof my invention is to provide a device of the type described in whichthe magnetic rotor will rotate through the shortest angle to the desiredposition.

In accordance with the features of my invention, my improved rotaryelectromagnetic positioning device comprises a magnetic rotor havingnorth and south` poles mounted within a stator having a number ofdistributed coils according to they number of positions, all of whichare energized simultaneously in a selected arrangement to rotate themagnetic rotor to any selected position, the coils'being arranged withrespect to each other and interconnected in such a man-V ner as tocreate a iield of high power for each of the number of positions forwhich the device is made. y

In a preferred construction my rotary electromagnetic positioning devicecomprises a magnetic rotor having opposed poles at right angles to itsaxis'of rotation, means for selectively producing a magnetic field at anumber of positions around the axis of the rotor, said means including astator ring of magnetizable material surrounding the rotor. a coilcarried by said ring for each position for which the device is made,said coils being arranged in series around said ring in regularnumerical order, each coil having two substantially spaced sectionsparallel to the axis of the rotor, corresponding sections of the coilsbeing arranged around the ring in regularly spaced relationship, andcurrent conducting means interconnecting the coils in closed series.

, Means is provided for alternatively connecting 2 y 4. one of the leadsfrom a current source with each of the means interconnecting adjacent pcoils. WhenV a current source is connected to a selected pair of saidmeans the rotor will move to a definite position because of the fieldcreated in the stator. In order to insure rotation of the rotor 'to aposition from a previous position I advantageously provide rmeans forcreating an eccentric magnetic field in the stator. This result may,however, be obtained by other means as explained hereinafter. Myinvention includes other features, objects and advantages which will bedescribedf and pointed out hereinafter in connection with .theaccompanying drawings forming a part of this application and showing anillustrativelembodimentV of the invention.

In the drawings: l Fig. 1 is an elevational view showing the outerstructure of a rotary electromagnetic positioning device according to myinvention.

Fig. 2 is an enlarged fragmentary view taken on the line 2--2 of Fig. 1showing in cross-section the arrangement of the coils in the slots ofthe stator. Fig. 3 is an enlarged diagrammatic view"partly in sectionshowing the magnetic rotor,` the stator, the position of the coils inthe stator, and an example of the circuits'and connections and currentflow for one positionof the rotary magnet in an eccentric field. l i

Fig; 4 is a broken view partly in section Mshowing a modified form ofmagnetic rotor. Tf

The illustrated embodiment of the rotary elec.- tromagnetic positioningdevice as shown in Fig. 1 of the drawings comprises a cylindricalcasingv 20 having a mounting base 2l and'heads Ziehaving bearings inwhich a rotary shaft i3- is mounted. a pair of cables 24 and 2c eacnincluding a piuraiity of current leads extending from the device andconnectedintoa switching mechanism'jz. shown in Fig. 3. The mechanism tobe operated by the rotary electromagnet is connected to vthe extendedportion of the shaft'23 by any suitable means, such as gearing,arms,"switching means and flexible or other sharts suitable i'orthepar-` ticular purpose. The elements ofthe device mounted inthe icas"-ving shown in Fig. l constituteastator ringe-1 oi iron orY othermagnetizable material heldin fixed relation to the casing 26 byperiplirally spaced lugs 28 in a known manner as illustrated intheenlarged detail in Fig. 2. The ring 2l is concentric with thehshaft 23,which,`qas shown in Fig. 3, has iixedthereto a permanent-'sym'-metrically balanced magnet 29 having north and south poles indicated atN and S.

The stator ring in the particular example shown in Fig. 3 is providedwith I2 slots numbered I to I2, parallel to each other and parallel tothe axis of the ring. These slots, as shown, open through the innerportion of the ring and are wide enough to permit ready insertion of thecoils of thel stator. The pole endsof the magnetic rotor 29 are curvedas shown, and extend closely adjacent to the inner arcuate surfaces ofthe poles p (Fig. 2) of the stator ring 21 which alternate with theslots. The magnetic rotorY 29 may be as thick as the stator ring 21 isYwide.;- The stator ring 21 carries 12 coils numberedV Ic to I2C, eachhaving two k sections,VextendirigHY parallel to the axis of the ring.The` present stator has been wound eccentrically for'the purpose ofobtaining an unsymmetrical magnetic lleld when energized and accordinglythe coils in thellustrated embodiment have a fullpitch less one statorslot. For example, as regards coil Ic, thelparallel sections' arelocated in stator slots' I and, and for coil 2c vthe parallelsectionsvare locatedin slots `2 and 9, and so on; In winding the statorsymmetrically to obtain a symmetrical magnetic rileld when energized afull pitch would belemployed so that the sections of` coil Ic would belocated in lslots I and 1, and so'on, with the sections `for each coillbeing angularly displaced 180 degrees. In winding coil Ic and the othercoils, as disclosed. in Figure 3, a wire conductor is passed throughslots I and 8 to lform a loop and the winding is continued until coilvIchas the desired number of turns. o The last turn from slot 4Bis thenpassed through slots 2 Yand 9 to'form coil 2c and the windingis'scontinued until this second loop is completed. Theremainingcoils areformed in Aa similar manner, allA being wound in thesamej direction, andupon completion of coil I2c the last turn leaving slot 1 is connected tothe iirst turn entering slot I of coil Ic., Accordingly, the coilsprogress in numerical order around the stator and the said coilsjareconnected by the conductors to form a closedseries'. Theslots in whicheach coil section is mountedis alsoshown by the following table:

CoilIcLihaslotsland 8 Coil Zcinfslots 2 and B Coil 3c.in.slots Sand, IU:Coil 4c in slots 4 and II Coil-5c in slots 5 and I2 Coil 6c in slotsandI` u Coilf'Ic in slots 1and2 Coil 8c in slots 8 and 3 Coilcin slots 9and 4 Coil I Dein slots I 0 and, 5 Coil I Ic in slots II and 6 V CoilI2c'in slotsl2 and 1 The slots in the ring 21 are lined with insulation30 and the bundles of windings comprising each coil are covered with alayer of insulation 3|. Each coil, as inthe case of electromagnets andsimilar electromagnetic devices, comprises a multiplicity of turns ofinsulated copper wire as indicated in Fig. 2. The position of the coilsin the Aslots is shown by circles in Fig. '3, it being understood thatsince each coil is a loop, it will comprise in addition to the sectionsextending through the slots, respective side portions which liealong theopposite end faces of the Yring 21 p artlysor'completely outside theslots. AFor err--` ample, sincecoil Ic has sections mounted slots..a'nfd ,ihg-Qther perdons ,Qf the. Lcoil will lie '4 opposite eachother in an arc along the respective end faces of the ring 21, outsideor partially outside of slots 9 to I2.

In Fig. 3 the portions of the coils lying along the under face of thering 21 are represented by single dotted lines; while the portions ofthe coils lying on the upper face of the ring 21 lie over thecorresponding portions on the opposite or under side of the ring.This'relationship is shownfinFig. 2,1in which-'the portions of the coilslying along the underside of the ring are indicated by dotted lineswhile the corresponding portions lyingalong the upper side of the ringare in full lines.

The rotary electromagnetic positioning device showngin the-.illustrativeexample is a 12-position device, the stator ring having 12 slots andcarrying V12 coils arranged so that portions of two-different coils aremounted in the same slot in the particular relationship described above.When itis desired, to rotate the shaft23cand magnet 2,9 to'a particular.angularpositionof the twelve positions for wwhichthedeviceisconstructed, all coils ,are energized ina relationshippeculiarto that position,.the interconnections between the differentcoils being. shownin full lines extending from the circlesrepresenting-the coilsito points outside ythe ring 21;..l

The full line. connections referred tohave been drawn lwith arrows andconnected 11p, toilliisl trate the circuit connections for movingY therotary magnet VESVtotherposition shown. The device is connected Kupwithlaijcurrent source, such as a 2li-volt D. C. generator or battery.. andcurrent is supplied through a current supply line 32 yto the multiple.,switching mechanism26 which is provided with a separatevdoublerpoleswitch for eachy position, respectively` numbered Is to I2s.. Each ofthese switches,hasjacon-f nection tothe plusand minus leads of the,curient supply line 32. The cables 24and 25 each contain twelve wiresrespectively connectedin pairs to the switches. In the illustratedem-vbodiment each coil has connection with two current leads indicated by-.d4and respectively. For coil Ic the first turn of theconductor enteringslot ,I has connection tothe inlet lead Id. The last turn `of theconductor leaving slot 8 has connection to the exitlead V1.9:. Likewisefor coil 2c the iirst turn connectswithinlet lead'Zd and the lastturnwith exitlead 8a: and so onforll thecoils.

In the j circuit (arrangement. shown in Fig.. 3, the vswitch Is has beenclosedl-and. current fis supplied from the minus side of the line,through the wire Id comingout of the cable 24. Current supplied to thiswire is divided throughtwo sets, of coils through which it ows in twocircuits of unequallengths, onethrough a wire I a--leading directly [tothe coil.Ic,while the other-,leads to the coil I2C. It will be notedthat the branch wire- Ib leading off: to the leftiromthejline Id .runscounter-.clockwise,halffway around the ring21 to enter the top of thecoilv I42c,-so that thepurrent flows downwardly `therethrough in theslot 1. When la full-line current lead endsdnraqblack arrow, `in acircle krepliESeIiting a portiongota coil., the currentin vthat portionof. thegcoilf` flows. downward from the surface ofthe` sheetofdrawings;whereas, where a dotted,linelcurrentlead terminates in an outlinearrowin a circle-representing a portion of Aafvcoil, the current. in.that portion Yflows upwardly-l and Tleaves ;the...coil` through a.. fulllineconneciine wire..- V

The portion@ the current flowingthroughthe wiresllI-d and .la` to "coillc, lea'v'esthat icoilffrom the slot 8,' asin'dicated, and flows inseries'through the succeeding coils 2c to 1c', inclusive. The por-- tionofthe current enteringcoil l2c1from the line Id through branch lb iiowsin successionfthrough the coils |20 to 8c, inclusive. The two .currentpaths lfrom the final coils 1c and' 8c meet in an exit line la: whichenters the `cable' 25 andis connected to the switch is and tothepositive current lead of the line 32. Thedivided paths of flow throughthe two sets of coils, .'l'in one case and in the other, can be readilytraced from one coil to the next by following.V in the direction of thearrows on the full and dotted lines.

`A separate current inlet and outlet line con-` nected to the respectiveswitches Is to l2s, is shown for each position, the inlet lines beingrespectively the lines. ld to |201, inclusive, leading from the cable24, and the current exit linesbeing I'to IZ-, inclusive; leading intothe cable 25, it being understood that only one pair of these lines isconnected at a time and that while the others lead into respectivebranching linesthey do not affect the flow of current from one coil toanother through the branching lines. For example, as shown in Fig. 3,the current flowing from the outlet of coil Ic, slot 8, flows toward theoutlet line 1x, but since the switch 1s is open the current flowsclockwise to the line 2d, and then into the coil 2c.

The current outlet wires for the different positions and numbered la: tol2rr, are respectively connected into the switches Is to f2s.

In the illustrated example shownin Fig. 3, the

magnetic field created in the poles of the stator by the coils in eachslotis rdetermined by thedi rection of current through` the portionsofthe coils in that slot. The full line or black arrows in the circlesrepresent north magnetic fields; while the dotted line or outline arrowsrepresent south magnetic fieldsV It will be noted, therefore, that coilsin slot I and 2 create no magnetic iield in the intervening pole, sincethe two coil sections in each cancel or neutralizev each other. Thecoils in slots 3 to 'I create north magnetic fields, or the sum of thesecreate an intensive north magnetic eld attracting thesouth pole ofrotary magnet 29. 0n the other hand, the coil sections in slots 8 to I2create an intensive south magnetic field in the stator poles attractingthe north pole of the rotary magnet 29. Thev eld created by the coilsections in the ve north pole slots is equal to the *fieldcreated by thecoil sectionsin the iive-south pole slots, but these fields are notdivided equally by the north-southk line through the axis of the rotarymagnet 29. An eccentric field or iields `are therefore created, and theinstant the switch Is is actuated, the rotary magnet 29 assumes theposition shown, and stops dead ina balanced position at the point ofmaximum magnetic iux.

Whenever any one of the switches AIs to |23 is closed, as for exampleswitch is, as illustrated in Fig. 3, the stator 21 is always dividedinto two poles, as for example the north and southpoles, respectively onthe right and left sides of the dotand-dashline A-A which 'is at rightangles to the north and south axis of the rotary magnet and extendsthrough the 4null point between the neutralized coil sections in slot land 2.V

When the switch is is opened and the switch 2s is closed to sendcurrentthrough the lines 2d.v and 2m, the rotary magnet 29 A rnovesclockwise tothenext position.; y 'The magnet 293can be caused to move from oneposition to any othergofthe;

6. twelve positions, `includingTmovenient through 180", independent ofall other poles or positions, because of the eccentric character 'oftheeld created by the closing of `any position switch: YIn

these operations the rotor 29 will rotate throughl the, smallest Vanglepossible from one position to another selected position.

. The means or arrangement for creating eccentric or unbalanced elds inthe stator is particularly advantageous because it insures the ro-vtation of the rotor through an angler of $180". Tests have veriiiedthese results and have shown that where the leldin the stator issymmetrical with respect to a line through the axis and,-poles of therotor,` the rotor will not always turnvwhen the fields `are reversedkbecause of the balanced condition. The eccentric field arrangementtherefore avoids the necessity of having to take two or more steps toinsure rotation thro.ugh.180. An electromagnetic positioning devicemaybe constructed according to the present invention without including themeans or arrangement for forming eccentric elds in the stator, which therotor will rotate from one position to a'position at 180 therefrom, byproviding a magnetic rotor having approximately the structuralarrangement shown in Fig. ,4 of the drawings. In this view thestatorring 2 1 and coil arrangements are exactly the same as that shown inFigs. 1 to 3. except that the switch connections are made so that anequal number of coils are traversed in each set by the current suppliedto the coils of.

the stator. n

This is accomplished in the illustrative example shown in Fig. 3 bysupplying current through the the line Id and using line |23: as thecurrent outlet, instead of the line Ix. When the connections are made inthis way the coils in the slot l neutralize each other and the coils inthe slot 1 neutralize each other, as will `be readily seen by tracingthrough the paths of current flow from the line id to the line I2.r.Current flows through the branch la and in succession through the set ofcoils Ic to 6c; while current iiowing through branch lb flows insuccession through the set of coils I2c to 1c. The outlet line I2isconnected into the final coils Bc and 'lc of the two sets. This change,as will be noted, reverses the current in the coil 1c, thereby changingthe arrow in the-lower circle 'Ic to outline, andthe onein the uppercircle 1c to black. l In Fig. 4 the rotor is mounted on a shaft. 23 andcomprises a permanent magnet 29a having complementary beveled pole endsurfaces 34 which recede from the pole end edges 35 where the magneticforce is the strongest because of the closerproximityof these edges tothe poles of the stator. When the rotor magnet is constructed as shownin Fig. 4, the edges 35 which are parallel to and closest to the statorwill not line up in the center of the magnetic elds produced in thestator, because of the surfaces34. While these surfaces 34 recede awayfrom -'the inner circumference of the stator, they nevertheless havesomeeffectupon the orientation of the rotor so tnatthe center of thefields of the opposite ends of thefrotor magnet 29a is approximately onthe dot-and-dash line B-B and perpendicular to the dot-and-dash A-Aextending through the null points of the stator. perpendicular line BeBis not parallel t0 the sides of the ro-tor magnet 29a but cuts `thesur-` faces 3 4k at an acute angle inwardly of the edges 35.- Thesurfaces 34 need vnot be straight but-'may recede in anarcfrom-.therespective.edges 35 to' This animee.

mdualiyfincreaseathe d,spacing fronrzthe stators; Ii; it :is 1- desiredp to rotate.: the magnet .29a througlipaniangle'of 180.; the fields of.the-statorI are exactly reversedr When-this; occursinzthe arrangement:shown in- :Fig. 4, north 'and south magneticnelds are `createdrespectivelynopposite the north and south poles .of Vthe magnet ZSajandthe. repelling forcesthus.applied instantly tact upon Vthesloping.surfaces 3ft@ .throw the. rotor oir: balance andV thereby initiates:its; rotation jacent *tof the Aedges @3 5 of the rotor. magnet fandeffectthe startingxof its rotation.-. As soon-ras the rotor-is .ofbalance, it moves quickly to the res verse position.;

Either of. the means or arrangements described may. Ebe. utilized forinsuring lrotationV of the rotor through: .an angle of :180 1inoneoperation;` or other. means or changes maybe vvprovidedforaccomplishing .this result.

Ineither. /iormA4 of. fthedevice. all 'the coils-ofthe. stator unit areenergized for-V each lposition and therefore a maximumof..'electromagnetic energyfis provided.l which in turndevelops amaximum `torque for. f the rota-tion of the magneticroton It hasbeen4foundrthat the torque developed by device-.constructedaccording to-the ipresent invention is equivalent tov that 'of a motor havingtwice .thephysical size and-thesame elec-` trical characteristics.

When it is' desired to make-a rotary-'electromagnetic positioning.device 'for' any particular? number.. of 'positionsfandy for aparticularpur'- pose,-:it will .be understood-=thatfthe sizeof lthe device will be.-determinednin general by the torque requiredand that the number-of--positionszwill determine the number of coils and Vslots ofpthestator. The illustrated system of connections shownin Fig. 3 anddescribedherein should enableanyone skilledin the art to interconnectthe vcurrentleads for the rtwo-sets of coils so as to achieve theresults described;

The-.positioning device advantageously hasI an l even number ofpositionsor poles sothata distinet null .point or points is formed, and the coilsmay aber divided into current paths of unequal lengthfinwhichlone pathwould include two more coils than the other path; If a device isdesiredwithganzodd number of positions, asffor example, a.25.;posi-tionadevice;-v it `maybe-- madeftvithi 26 positions andarranged sothat onefofs-the posi-f tionszisz not utilizedf Insorne-cases'the-v device ir maygbefmadewith' an'4 odd..numberofpositions; However, when it is energized to produce an eccentric. field` .therev Willi onlyrlbe 'one pair ofcoil sectionsWhichneutralize-each other to provide a null point.:

FigrB of the vdrawings showsseparate connecf tions respectively to the.cable 24 and 4to the cable jfor the different postionsf Asomewhat sim-vplied :form of arrangement can 'bef providedin which the `electricalconnectioigbetween adjacent coilss usedat oneitimelor a Acurrent inletcon nection and at another time in 'obtaining-a dif-v ferentvposition,ffo'r a current outlet connection: Noteffor example, that thecoil lc is' connected iii-:series with the coll2e bythe connecting Wire[band that the two endscf the Wire ib are-re` spectivelyrconnected--tothe cable l24 by'the lead'4 Id'andto the cable 25 by the lead Btc. Theleads- I d Aand `6.1:;however, :are neverl'used at the same time.;and-.therefore .f.one...cr.: eitherxotthemfcouldbe:usedztozmakeethesconnectionszto vthe twoadlfs ferentgcurrentsleads.atfdiierent `times fior rliilereent positionsc: Theicircuits and.function or the device.' however; are more .conveniently illustratedin*thermannerzshownainL Fig. 3. l

While the device .of :the-.present 'invention hasy beemillustratedin'yconnection `with Aa permanent magnet 29 ort29a, it is .to-.beunderstood that the rotonmaycomprise an electromagnet. Inrelativelysmall'devices .which have been mada-however, it'hastben'foundlconvenient :and-.advant-` geous to mplcyiapermanent magnets.

WhatfI claim is :.1

1. Inv a .rotaryelectromagnetic positioningagde-i Vviceincludingamagnetic rotor.` having :opposed poles at yright angles .to itsaxisgoirotation, means for `selectively producingamagnetic: neld at va numberofpositions` around .theaxisnf the rotor,y said means 'including astator. 'ringfoff'magnetize able materiall .surrounding the rotonacoi'l'carried by saidvringforeach position'for Whichzthe .device is`made; said coils beingV arranged; around. said ring 4in regularnumerical orden. each coil having twoA substantially spaced sections.parallel to .the

1 axis ofthe-rotor, corresponding sections oftthe coils being 'arranged'aroundf the ring Ain' regularly spaced' relationship, andV currentconducting means-interconnecting theVv coils in closed series;

2. A 'device as claimed in claim 1 characterized in that the saidparallel sections of each coil are respectively mounted vadjacent afparallel section of twodiierentcoils.

3. A device asfclaimedin-'claim 1 characterized in rthat? said' -ccils-aref'woundf inv the same direction:

4. -Afdevic'e kas claimed'infclaim 1 'characterized by includingmeansffor connecting selected pairs of said current conductingmeans-with a-source of D. C.`current for energizing `the poils.

' 5." A rotary-electromagnetic positioning-device comprising a magneticrotor having opposed poles at Yright angles to its Iaxis of rotation;Ameans for selectively producinga magnetic field at anum-1 ber ofpositionsaround the axis of the rotorfsaid means including 'a statorring of magnetizable material-*surrounding'theroton a coil having Va.

multiplicityof VturnsY carried by said ring foreach' position for AWhichthe ydevice is made, said-coils havingoverlapping relation and beingarrangedaround said-ring in regular numerical order,l eachcoil havingtwo substantially J 'spaced-1 sections paralleleto the axis'oftherotor,` corresponding parallel'v sections ofthe different coilsbeing; arranged" aroundv the'ring in regularly Yspaced-relationship;'electrica1' Aconductors interconnecting the coilsinfclosed series; and a current leadcon`' nectedinto 'each-'of the saidconductors;`

6. A'devicejas-claimed in claim 5 characterized by includingjmeansfforsupplying current to one 0I* said current leads whereby `current: issupplied through the conductor attached thereto inparalf lel totheadjacent coils connectedby'the 'conductor,"and-a common 'current outle'tconnection frcm'f'other adjacent coilsof series.

7. lA devi'ce; as Yclaimed'in claim 5- characterized by includingmeansfor supplying current to one of said currentleads whereby current isdistributed Vin'paralll through' the' conductor to vwhich the lead isattached and l'tov the adjacent coils'r interconnected bythe conductor:and acommon current outlet connection from lanother fpair "of adjacent"coils locatedfat apositi'on in the series ofY coils dividing it intovpathsof unequal-lengths,` whereby an Y`eccentric magnetic field isestablished inithesta'tor." Y

8. A rotary electromagnetic positioning device comprising a rotor havingopposed poles at right angles to its axis of rotation when magnetized,means for selectively producing a m-agnetic eld at a number of positionsaround the axis of the rotor, said means including a stator ringsurrounding the rotor and having a magnetizable element for eachposition for which the device is made, a coil for each of saidpositions, said coils being arranged around said ring in regularnumerical order, each coil having two substantially spaced sectionsparallel to the axis of the rotor, corresponding sections of the coilsbeing arranged around the ring in regularly spaced relationship at saidpositions, electrical conductors interconnecting the coils in closedseries, a current lead having electrical connection to each of saidconductors, and means for selecting a pair of substantially separatedcurrent leads to energize said coils. k

9. A device as claimed in claim 8 characterized in that the currentleads are arranged in pairs for dividing the series of coils into twocurrent paths including an unequal number of coils.

10. A device as claimed in claim 8, additionally characterized in thatthe poles of the rotor have end surfaces at an acute angle to the polaraxis of the rotor.

11. In a rotary electromagnetic positioning device, a stator ring, amagnetic rotor providing polar projections and mounted for rotationwithin the stator, said stator having a plurality of slots parallel toits axis, a coil for each slot comprising a multi-turn loop each woundin the same direction and having two parallel sections disposed indiierent slots of the stator, said coils being disposed around thestator in regular numerical order and being so arranged that each slotcontains a parallel section of two different coils, a conductorelectrically connecting the end terminal of each coil with the startterminal of the next adjacent coil in numerical order whereby to connectall the coils in closed series relation, a current lead connected toeach conductor, and means connecting a direct current source to aselected pair oi current leads for energizing the coils, whereby currentis caused to flow in two parallel paths each including its respectivecoils to produce opposed magnetic elds on respective sides of thestator, and whereby all the coils are energized for each position withcertain coils having a parallel section in each magnetic field as aresult of the disposition of the sections around the stator and currentilow through the same.

12. In a rotary electromagnetic positioning device, a stator ring, amagnetic rotor having polar projections and mounted for rotation withinthe stator, said stator having a plurality of slots parallel to itsaxis, an inductive winding for the stator comprising a multiplicity ofcoils equal in number to the stator slots, said coils being wound in thesame direction and each comprising a multi-turn loop having two parallelsections located in different slots angularly spaced approximately 180degrees, said coils being disby to connect all the coils in series, acurrent lead connected to each conductor, and means connecting a directcurrent source to a selected pair of current leads for energizing thecoils, whereby current is caused to ilow in the inductive winding in twoparallel paths each including its respective coils to produce opposedmagnetic fields on respective sides of the stator, and whereby all thecoils are energized for each position with certain coils having aparallel section in each magnetic field asa result of the disposition ofthe sections around the stator and current iiow through the same.

13. A rotary electromagnetic positioning device, a stator having coilreceiving slots, a rotor adapted to be selectively positioned at aplurality of locations around the stator, an inductive winding for thestator comprising a plurality of coils disposed around the stator innumerical order and connected in series by conductors each connected toa pair of adjacent coils, said coils each comprising a multi-turn loophaving two parallel sections, the parallel sections of each coil beingspaced to locate the same in diferent slots and each stator slot havingparallel sections of two different coils, means for establishing opposedmagnetic fields in selected positions around the stator to index therotor comprising ,switch mechanism for connecting selected pairs ofconductors to an energizing current, whereby ilow oi current in theinductive winding is divided into two parallel paths including a groupof coils for each path determined by the current inlet conductor and theparticular conductor selected for the current outlet, and whereby allthe coils are energized for each position with certain coils having aparallel section in each magnetic eld as a result of the disposition ofthe sections around the stator and current flow through the same.

14. A rotary electromagnetic positioning device as dened by claim 13,further characterized in that the current inlet conductor determines thecoil groups and the current outlet conductor determines the number ofcoils in each group, and wherein for each position a majority of thestator slots contains a parallel section of a coil of one group and aparallel section of a coil of the other group.

HOWARD B. ACKERMAN.

REFERENCES CITED The following references are of record in the nle ofthis patent:

UNITED STATES PATENTS Number Name Date 1,371,096 Howe et al Mar. 8, 19211,653,946 Clausen Dec. 27, 1927 1,949,145 De Luca Feb. 2'7, 1934;

